MOBILE, Alabama – On the eve of a marriage fraud trial, a federal judge Thursday handed prosecutors a victory in a dispute over what authorities must prove to sustain a conviction.

At issue was whether the defense could argue to the jury that prosecutors must prove that the “sole” reason for the August 2009 marriage between Andreas Andreasen Jr. and his foreign wife, Katerina Petrasova, was to provide legal residency status for her.

The defendants are to be tried in separate trials, with Petrasova facing a jury beginning Wednesday and Andreasen the following week.

Chief U.S. District Judge William Steele granted a request by prosecutors to prohibit defense lawyers and others involved in the case from making the “sole reason” argument at either trial. He cited two appellate court rulings that backed the prosecution interpretation of the law.

Both cases “support the proposition that a defendant can be convicted under (the statute) without proof that evading the immigration laws was the defendant’s exclusive purpose,” the judge wrote. “While neither appellate court provided much explanation for its conclusion, such reasoning exists.”

The position of the U.S. Attorney’s Office represents an about-face of its interpretation of the law in a different marriage fraud prosecution just two months ago. In that case, prosecutors took the position that the law did require them to prove that a desire to evade immigration law was the sole reason for the union.

“While it may seem odd that the government would so quickly abandon this position in favor of its opposite, no legal principle precludes the government from doing so,” Steele wrote.

An attorney for Andreasen, James Scroggins, could not immediately be reached for comment. In a court filing, he pointed to an administrative manual governing applications for permanent residency. That document states that a petition may be approved “if the marriage is valid and was not entered solely for immigration purposes.”

But Steele wrote that an administrative agency’s manual does not carry the weight of a law passed by Congress.

“Certainly, the defendant does not explain how the manual – which does not rise to the dignity of a formally adopted rule – could control or even influence the interpretation” of the statute, Steele wrote.

Petrasova’s lawyer, Arthur Madden, took a different approach in making a similar argument. He asked Steele to prohibit prosecutors from arguing that they need only prove that the immigration issue was “a” reason for the marriage but not “the” reason.

Steele wrote that he would not consider the request, though, because Madden did not make the request in a formal motion.

The indictment alleges that Petrasova, a native of the Czech Republic, came to the United States on a visitor visa in April 2002. She and Andreasen, an American citizen, married on Aug. 18, 2009.

Later, according to the allegations, the couple signed immigration forms and traveled to Atlanta to be interviewed by immigration officials even though it was not a legitimate marriage.

In convicted, the defendants face a maximum of five years in prison, although both likely would be eligible for probation under advisory sentencing guidelines. Petrasova could be deported.